Creating the effect of a Flip Flop gate using Logic Bricks
From the way you wrote your question, it sounds like you want to toggle between camera views. You can use a Boolean property, and have a keypress toggle that property to true or false. Then, if that property is true, the First Person camera will be activated, and if that property is false, the Third Person Camera will be activated.

This logic setup is one of the simplest you can use to toggle between two camera views:



Of course, you could use an integer property and a few more sensors and controllers to cycle through several camera views, instead of using a Boolean property (which can only be true or false) for the two camera views.